Applications of Thermodynamics to Geological Systems

Temperature and pressure effects become important in chemical systems of geological interest. Also, the chemical nature of the system is often not well characterized. Nonstoichiometric compounds and solid solutions are often present, with complex silicates frequently playing an important part. 

In spite of these complications, thermodynamic techniques can be very useful in understanding geological processes. We will consider an example involving a rather simple substance, followed by an example that demonstrates the usefulness of thermodynamic analysis in a more complex system. 

The equilibrium constant can be calculated from thermodynamic data. Robie et al9 give the standard state thermodynamic data at T = 298.15 K, which we summarize in Table 15.1. The value of C° m for C03 (aq) has not been determined experimentally. Nordstrom and Munoz10 used estimation techniques to obtain the value of —403.3 J K 1 mop1 given in the table. 

In calculating the solubility, Nordstrom and Munoz started with the equation 

They also did an extended treatment in which they assumed a constant ArC°, so that AXH° varied linearly with T/(K), and obtained the equation 

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